Gaskets essentially are used to seal and prevent leakage between two parts. Exhaust manifold gaskets for internal combustion engines seal any gaps and prevent leakage when the mating surfaces of the cylinder head and the exhaust manifold are bolted together. The gaskets may be made of layers and one or more of the layers may include a bead. Sealing the joined area between the parts can be difficult because the cylinder head, manifold and gasket all move due to pressure and temperature fluctuations. There are also problems due to thermal expansion and thermal contraction, which occurs when the temperature varies in the cylinder head and the manifold.
Thermal motion, resulting from hot exhaust gases, increasing combustion pressure, steep thermal swings, and sheer stresses are created in the joined area between the cylinder head and the exhaust manifold increasing the risk of horizontal motion and shifting of the gasket layers, such as in a multi-layer steel (MLS) gasket. When this occurs, the layers shift and the mechanical beads in the gasket layers can become misaligned. This reduces the sharing capabilities of the beads located on the various layers, and the misaligned beads may induce unusual stress concentrations.
There are also multiple openings in the cylinder head and the manifold for exhaust gases and bolts holes. The areas around these openings are known to be put under additional stresses and leakage is common due to movement and misalignment of the gasket layers.
Traditionally, the various gasket layers are aligned and held in place during gasket assembly by welding, eyeleting or form-locking. The eyeleting and form-locking methods both add thickness to the gasket and therefore must be located outside of the joined area, which is not ideal. While welding does not necessarily add thickness to the gasket, the weld spots may crack and/or break due to horizontal hardware motion which allows the gasket layers to shift.
In view of the foregoing disadvantages of the prior art, it would be advantageous for a MLS gasket to be able to prevent or resist horizontal motion and misalignment of the layers to the extent that it negatively affects performance of the gasket.